1. Field of the Invention
The present invention relates to a speaker apparatus for converting an electrical signal into a sound signal.
2. Description of the Related Art
A conventional speaker apparatus converts an electrical signal into a sound signal according to Fleming's right-hand rule, which explains why a conductor located in a magnetic field has a current flow moving in a certain direction due to an acting force. An example of a conventional speaker apparatus is illustrated in FIG. 1.
As illustrated in FIG. 1, the speaker apparatus has a permanent magnet 30 placed between top and bottom metal plates 64 and 63. The opposite side of an inner surface of the permanent magnet 30 is an inner magnet 40 that protrudes vertically such that it has a certain gap from the inner surface of the top metal plate 64.
A bobbin 51, wound by a voice coil 50, is inserted between the permanent magnet 30 and the inner magnet 40. The top of the bobbin 51 is connected to the bottom of an acoustic vibrating plate 20. The top of the acoustic vibrating plate 20 is fixed to a speaker frame 10, which is fixed to the top metal plate 64.
Here, an edge 65 is formed between the speaker frame 10 and the acoustic vibrating plate 20 for preventing a split vibration of the acoustic vibrating plate 20, while a damper 60 for regulating the vibrational range of the acoustic vibrating plate 20 is formed between the bobbin 51 and the speaker frame 10. Additionally, a dust cap 67 that prevents the inflow of external dust is disposed on the top of the bobbin 51.
With this configuration of the speaker apparatus, a magnetic field is generated between the permanent magnet 30, the top and bottom plates 64 and 63 contacting the permanent magnet, and the inner magnet 40. Additionally, an electrical current is applied to the voice coil 50.
A force acts on the bobbin 51, wound by the voice coil 50, due to a current flow of the voice coil 50 and a magnetic flux flowing through the permanent magnet 30, the top and bottom metal plates 64 and 63 and the inner magnet 40.
That is, the bobbin 51 vibrates up and down according to Fleming's right-hand rule. The vertically vibrating bobbin 51 causes a vibrational motion in the acoustic vibrating plate 20 connected to the bobbin 51, so that a sound is generated.
However, a problem occurs in that the acoustic vibrating plate 20 cannot vibrate in the same phase when the acoustic vibrating plate 20 is vibrated by the bobbin 51 disposed in a central portion of the acoustic vibrating plate 20. That is, the top and bottom of the acoustic vibrating plate 20, being respectively connected to the speaker frame 10 and the bobbin 51, have different vibration speeds, which generate a split vibration. The split vibration affects the sound pressure of the speaker apparatus and causes an impediment to uniform sound quality.
Accordingly, a need exists for an acoustic vibrating plate that vibrates in the same phase to provide an improved speaker apparatus having a high acoustic efficiency.